The second problem ("'this' expected...") comes because in Scala, auxiliary constructors must always call another constructor as their first statement. So your constructor could start with this(), for instance. For more details, see Section 6.7 in Programming in Scala.

The default constructor is the one you define when you declare your class

Ex:

class greeting(name:String) { ... }

You can also define the default constructor to take no parameters like in your code

class greeting { ... }

Then you can add extra constructors. All constructors you add to the class need to call another constructor as the first statement of the constructor. If you omit that you get the "this expected but identifier found".

In the code above
new classconstructor() does nothing because the empty constructor doesn't have body.
and
new classconstructor(200) executes the empty constructor + the new one where you can add extra code such as a call to moveNext() method. In this case this one prints 200 to the console.